1. Field of the Invention
This invention relates generally to computer controlled printing, displaying, or other presentation of documents which may have text, graphical components and/or images. This invention is more particularly related to a method and apparatus for processing selected pages in a hierarchically structured page description language.
2. Discussion of the Background
A Standardized Page Description Language ("SPDL") has been proposed and is being developed as an international standard by the International Standards Organization ("ISO"). The draft is known as ISO/IEC DIS 10180, labeled "Information Processing Text-Communication Standard Page Description Language" and is available through the American National Standards Institute ("ANSI") in New York, and is incorporated herein by reference. The current version of this draft is March, 1991.
One advantage of a hierarchically structured page description language is that when it is desired to have only certain pages or portions of a document printed or processed for presentation, it is not necessary to process the entire document but only portions of the document which are hierarchically above the desired portion of the document to be printed need to be processed. In contrast, a popular page description language such as PostScript.RTM. requires that the entire portion of the document appearing before the desired portion to be processed before the desired portion can be printed. For larger documents, this can amount to a significant amount of processing and communication time.
One of the required functions of a system conforming to SPDL standards as set forth in the current draft is to perform page selection in the Document Production Instruction. However, when pages are nested and the selection of pages to be presented requires pages to be selected from different hierarchical levels, it can become cumbersome to keep track of the nested levels of selected pages.
Section 6.6 of the March 1991 SPDL draft describes the high level structure elements used in SPDL. Of the three primary structure elements described in this section, the present invention is directed toward the picture and pageset. The draft SPDL standard states that a picture describes an image which can be considered as a single entity. It may be a page image or a partial page image. A pageset describes 0 or more pages.
While a page does not have its own SPDL structure element, a picture which is not subordinate to another picture is defined to be a page. Turning to FIG. 1 for an example of various pages, each picture illustrated in FIG. 1 is a page except for picture 116. All pictures except for picture 116 are subordinate to only pagesets and are not subordinate to other pictures. Therefore, each of pictures 104, 106, 112, 114, 118, 122, 124, 126, 132, and 134 are considered pages. While SPDL has detailed requirements for the picture and pageset structure elements, these details are unimportant to the understanding of the present invention.
The Applicant is not aware of any prior art systems which operate to select pages in a hierarchically structured page description language as required by SPDL. PostScript.RTM. by Adobe Systems, Inc. does not have a page selection capability. Interpress.RTM. from Xerox does have a page selection instruction, which is described in "Interpress The Source Book", pp. 352-354, 1988, published by Simon & Shuster. However, the Applicant is not aware of any prior art which shows the interaction of the page selection instruction with the hierarchical structure of a document in Interpress.RTM..
The problem which the present invention is concerned with can be seen in FIG. 1. The highest pageset of the hierarchical structure illustrated in FIG. 1, pageset 102, has pages 1, 3, 5, 7 and 8 selected for presentation. Pageset 108 has pages 2 and 3 selected for printing. Therefore, when selected page 3 of pageset 102 is to be presented, picture 104 corresponds to page 1, picture 106 corresponds to page 2, and pageset 108 must be examined to determine which picture is page 3. Picture 112 is not page 3 of pageset 102 as pageset 108 has only pages 2 and 3 selected. The first page of pageset 108 is page no. 2 which corresponds to picture 114. Therefore, page 3 of pageset 102 is picture 114.